An axial flow fan is an apparatus for rotating a number of radially arrayed blades to blow the air in an axial direction, and includes a shroud which serves to guide the air blew in by the axial flow fan directly backward.
The axial flow fan is used to ventilate a room or to feed the air into an air-cooled heat exchanger such as a radiator or condenser of an automobile in order to promote the heat dissipation thereof.
In the meantime, the shroud includes a number of strip-shaped and fixed guide blades which are arrayed radially from the central axis of the axial flow fan in order to raise the blowing efficiency of the axial flow fan. The guide blades converts the kinetic energy of the air blown from blades of the axial flow fan into pressure energy to raise static pressure thereby elevating axial blowing efficiency.
Hereinafter the structure of the axial flow fan will be described in more detail.
FIG. 1 illustrates a rear view of an axial flow shroud assembly adopted in a conventional condenser for an automobile.
As shown in FIG. 1, an axial flow fan 100 includes an annular fan hub 220 connected to a drive shaft 210 of a motor 200 and a number of blades 120 arrayed around and integrally with the fan hub 220. In the aspect of blowing efficiency, the axial flow fan 100 is typically installed in the rear of a condenser. Of course, the axial flow fan 100 may adopt a pusher type which is installed in front of the condenser in case that a sufficient installation space is not obtained in the rear of a heat exchanger within an engine room.
In the axial flow fan 100, the motor 200 turns the blades 120 in the rear of the condenser to blow in the air from the front of the heat exchanger through the heat exchanger to introduce the air rearward so that the air blew in by the axial flow fan 100 deprives the hot condenser of heat to cool the same. The axial flow fan 100 is generally made of synthetic resin, and integrally molded so that the fan hub 220 and the blades 120 are formed of a single body.
The shroud 300 functions to fix the axial flow fan 100 including the motor 200 with respect to the heat exchanger, and to introduce the air blew in by the axial flow fan 100 directly backward. The shroud 300 includes a substantially rectangular housing 310, a motor support ring 320 provided in the center of the housing 310 and a number of guide blades 330 arrayed substantially radially for supporting the motor support ring 320 with respect to the housing 310.
The guide blades 330 of the shroud 300 are connected to the motor support ring 320, and as shown in FIG. 1, obliquely inclined in the turning direction of the axial flow fan 100 to form air flow guide surfaces 332 of a predetermined area in order to vary the blown air in an axial direction to increase the quantity of the axially blown air.
That is, the guide blades 330 are straightly extended from the outer circumference of the motor support ring 320 toward the housing 310, and inclined at a predetermined angle θt with respect to the axial direction as shown in FIG. 2, as a schematic plan view of a single guide blade 330, so that the air flow guide surfaces 332 formed in the rear faces of the guide blades 330 can directly change the flowing direction of the air. As shown in the sectional view, the single guide blade 330 includes a leading edge 331 for introducing the air, a trailing edge 333 for exhausting the air to the outside and an air flowing guide face 332 connecting the leading edge 331 with the trailing edge 333.
The air flowing guide face 332 converts the rotation velocity component of the air into the axial direction to increase the axial velocity of the air thereby raising the blowing efficiency of the axial flow fan 100. That is, because the air blown by the axial flow fan 100 has not only an axial velocity component Uz but also a rotational axial velocity component Uth, the rotational velocity component Uth may lower the blowing efficiency if left alone. Thus, the rotational velocity component Uth is converted into the axial direction to enhance the axial blowing velocity thereby raising the blowing efficiency of axial flow fan 100.
The operation of the air flow guide surface 332 of the each guide blade will be described in more detail with reference to FIG. 2. Since an air particle in a flow field spaced from the center of gyration at any distance has an axial velocity component Uz and a rotational velocity component Uth by the rotational force of the blade 320 with respect to the axial direction, the air particle is blown toward the leading edge 331 of the guide blade 330 in a direction inclined to a specific angle θT in a rotating direction with respect to an axial line A.L which is actually parallel with the axial direction. Regarding the actual blowing direction, the air flow guide surface 332 of the guide blade 330, in view of the section in a breadth direction, is designed into a curve inclined at an angle θt (θt≦θT) in the counter-rotating direction of the axial flow fan 100, that is, the air exhausting direction with respect to the axial line A.L. Then, the air flow guide surface 332 refracts the air blown by the axial flow fan 100 in the axial direction thereby to increase the axial velocity of the air. The increase in the axial velocity of the blown air means the enhancement of blowing efficiency. As a result, in the design of the guide blade 330, the air flow guide surface 332 which is inclined in the counter-rotating direction with respect to the axial direction serves to enhance the blowing efficiency of the axial flow fan.
Considering the actual blowing speed, several approaches which can enhance the blowing speed through the variation of the configuration of the guide blade 330 have been studied in various aspects.
U.S. Pat. No. 4,548,548 discloses an invention which substantially limits an inclination angle with respect to an axial line of an air flow guide surface of a guide blade to further enhance the blowing efficiency.
That is, at a point in a flow field that is spaced from the center of gyration at a distance r in a radial direction, a velocity vector of an air particle has an axial velocity component A and a rotational velocity component R by the blade-turning force of the axial flow fan. The velocity vector Ao has an inclination angle T−Tan−1(R/A) with respect to the axial line. Regarding the inclination angle, the guide blade is so arranged that the normal line of the central portion thereof is inclined at an angle T/2 with respect to the axial line, and the air flow guide surface is curved to have a substantially arc-shaped section. In this way, the air flow guide surface introduces the blown air at the inclination angle T/2 in the center, and then refracts the blown air for the inclination angle T/2 to the axial direction. As a consequence, the axial velocity of the air blown by the axial flow fan is increased in proportion with the rotational velocity component R which is converted into the axial direction. That is, the air flow guide surface of the guide blade enhances the quantity of the air blown by the flow fan in proportion with the rotational velocity component of the air particle that is converted into the axial direction.
In the meantime, the air blown by the axial flow fan has a radial velocity component Ur by the centrifugal force of the axial flow fan in addition to the axial velocity component Uz and the rotational velocity component Uth. An approach for converting the rotational velocity component Uth and the radial velocity component Ur into the axial velocity component Uz to enhance the blowing efficiency is disclosed in U.S. Pat. No. 6,398,492 which was filed by the inventor of the present invention.
The guide blade of the present invention is arranged radially with respect to the central axis of the axial flow fan, and bent radially with respect to a radial line so that a leading edge line intersects perpendicularly with a lateral velocity vector Us that is the sum of the rotational velocity vector Uth and the radial velocity vector Ur. Further, the angle of incidence of the guide blade is the same as an air inflow angle Tan−1 (Us/Uz), that is the angle of the air introduced to the guide blade, and the angle of projection of the guide blade is curved at 0° with respect to the axial line.
The prior art as above can enable the use of a low power motor by enhancing the axial blowing efficiency in order to reduce the power consumption necessary for the air blowing as well as to restrain noises during the air blowing. However, since the angle of projection of the guide blade is 0° with respect to the axial line, the air passing through the axial flow fan is guided toward the engine in the rear in the axial direction of the fan colliding into the engine so that high temperature heat generated by the engine flows backward toward the heat exchanger such as a condenser to elevate the refrigerant pressure of the heat exchanger thereby disadvantageously degrading the performance of an air conditioning system.